Lithography is used to apply a desired pattern onto a lithographic substrate or part of a lithographic substrate. Lithography may be used, for example, in the manufacture of integrated circuits (ICs), flat panel displays, and other devices involving fine structures. In conventional lithography, a patterning device, which may be referred to as a mask or a reticle, may be used to generate a circuit pattern corresponding to an individual layer of a flat panel display (or other device). This pattern may be transferred on (part of) the substrate (e.g. a silicon wafer), e.g. via imaging onto a layer of radiation-sensitive material (resist) provided on the substrate.
Instead of a circuit pattern, the patterning device may be used to generate other patterns, for example a color filter pattern, or a matrix of dots. Instead of a mask, the patterning device may comprise a patterning array that comprises an array of individually controllable elements. An advantage of such a system compared to a mask-based system is that the pattern can be changed more quickly and for less cost.
Although lithography is conventionally used to image a pattern onto a silicon wafer, it may also be used to image a pattern onto any other suitable substrate. Substrates onto which patterns may be imaged include, e.g., glass substrates such as for instance relatively large glass substrates for flat panel displays, or plastic. Substrates of this type may be more likely to suffer from distortion than silicon wafers. Since lithography systems are often designed to project patterns onto silicon wafers, in some instances they may only be able to measure a limited amount of substrate distortion. This measurement may be insufficient in some instances for flat panel display substrates or flexible substrates.